This invention relates generally to tensioning devices and relates, more particularly, to means for tensioning a power transmission belt or the like connected between a drive wheel and a driven wheel.
A belt tensioning device with which this invention is to be compared includes a housing having an elongated internal cavity, a piston head slidably positioned within the housing cavity for separating the cavity into two variable-volume chambers for holding hydraulic fluid, a plunger joined to the piston head and extending through an opening provided in one end of the housing for movement with the head as the head is moved along the housing cavity. A spring is interposed between the piston head and housing for biasing the head toward one end of the cavity, and flow control means are associated with the two variable-volume chambers for permitting a substantially unrestricted flow of hydraulic fluid from one variable-volume chamber to the other variable-volume chamber as the piston head is moved by the spring toward the one housing end and which permits a controlled flow of hydraulic fluid from the other variable-volume chamber to the one variable-volume chamber as the piston head is moved against the force of the spring away from the one housing end. Examples of such belt tensioning devices are shown and described in U.S. Pat. Nos. 4,472,161, 4,539,001 and 4,708,696.
For use of such a tensioning device, one of its housing and plunger is mounted in a fixed relation adjacent a belt desired to be tensioned, and the other of the housing and plunger is positioned in cooperating relationship with the belt so that the spring acts between the housing and plunger to urge the belt in one direction and thereby establish spring-induced tension in the belt. If, on one hand, the belt is displaced in the one direction, such as by oscillatory forces generated during sudden acceleration of the drive wheel, the spring moves the housing and plunger relative to one another by a corresponding amount to compensate for the displacement of the belt in the one direction and thereby re-establish spring-induced tension in the belt. As the housing and plunger are moved by the spring to compensate for belt displacement, hydraulic fluid flows freely from the one variable-volume chamber to the other variable-volume chamber so that the movement of the housing and plunger relative to one another is substantially unrestricted. If, on the other hand, the belt is displaced in the direction opposite the one direction so that the housing and plunger are forced to move relative to one another against the force of the spring, the controlled flow of hydraulic fluid to the one variable-volume chamber from the other variable-volume chamber limits the rate of relative movement of the housing and plunger. As a consequence of the substantially unrestricted relative movement of the housing and plunger in the one direction and the controlled rate of relative movement of the housing and plunger in the opposite direction, forces which would tend to oscillate the belt are resisted and oscillatory motions of the belt are dampened by the tensioning device.
It is an object of the present invention to provide a new and improved tensioner of the aforedescribed class.
A further object of the present invention is to provide such a tensioner which is relatively easy to assemble and uncomplicated in construction.
Another object of the present invention is to provide such a tensioner which is economical to manufacture and effective in operation.
Still another object of the present invention is to provide such a tensioner having a reduced susceptibility of leaking hydraulic fluid.